The invention relates to control of aircraft equipment, specifically to control of a self-propelled nosewheel. The present invention relates to the field of aircraft interfaces, and in particular to interfaces controlling motorized aircraft wheels.
The use of small compact electric motors inside, or in close proximity to, an aircraft wheel, for direct drive, presents a problem relating to the provision of the required amounts of torque. Generally, for moving an aircraft from rest, the torque required is extremely high, so that the torque versus speed characteristics of the load, and the maximum speed characteristics of the load when driven, fall well outside the ideal predicted by motor scaling laws. This means that a motor sized to produce the torque necessary for direct drive of the load will be operating at well below maximum speed, and thus well below maximum power levels. The active materials of the machine will be underutilized, the machine will be far heavier than necessary, and the machine efficiency will be poor.
Gearing can provide a higher speed, lower torque motor with a higher torque option to enable a motor to be housed within a wheel. The wheel itself is expected to operate during takeoff and landing at much higher than normal motoring speeds. This presents a significant problem, because, in these cases, the wheels may be rotating faster than the motor and may accelerate the motor via the gearing system. Under these conditions, the motor would be forced to spin at much higher speeds than rated.
U.S. Pat. No. 3,711,043 to Cameron-Johnson discloses an aircraft drive wheel having a fluid-pressure-operated motor housed within the wheel and two planetary gear stages housed in a gear box outboard of the motor, the final drive being transmitted from a ring gear of the second gear stage, which is inboard of the first stage, to the wheel through an output drive quill coupled, through a disc-type clutch if desired, to a flanged final drive member bolted to the wheel.
U.S. Pat. No. 3,977,631 to Jenny discloses a wheel drive motor selectively coupled to an aircraft wheel through a rotatably mounted aircraft brake assembly in order to drive the wheels of an aircraft. The normally non-rotating stator portion of a conventional aircraft brake assembly is rotatably mounted about the wheel axle and is rotatably driven through a planetary gear system by the wheel drive motor.
A solution disclosed in PCT application WO2005/035358 discloses a mesh connected high phase order induction motor, situated in close proximity to, and preferably within, the nosegear. The mesh connection enables variable inductance so that the machine has a range of speed/torque profiles available.
Various guidance systems for aircraft taxi are disclosed in the art. The degree of automation in taxiing may vary.
U.S. Pat. No. 6,411,890 to Zimmerman discloses a method for the guidance of aircraft on the taxiways of the airport apron with position lights located on the taxiways and, possibly, other locations on the apron. It comprises the following components: a navigation system to determine the current aircraft position; a sensor on the aircraft to detect position and measure lights, reference information including light positions, a comparison of the path pursued by the navigation system with the reference information, and using the detected lights as waypoints for the navigation system. The method determines the current aircraft position more precisely than purely through the navigation system, and generates guidance information based on the determined aircraft position. The invention further discloses an additional sensor for the detection of lights and their position measurement. The latter should be performed with a precision of approx. 10 cm. Video cameras and scanners, for example which can be advantageously arranged on the aircraft main landing gear, are suited for this task.
U.S. Pat. No. 6,690,295 to De Boer teaches a device for determining the position of an aircraft at an airport, including sensors for detecting radio signals originating from a vehicle. The sensors are positioned at regular intervals from one another on parts of the airport which are accessible to the vehicle. The sensors are fitted in light positions of runway lighting provided at the airport on taxiways, take-off and landing runways and on platforms. The signal originating from a radio altimeter of an aircraft is used as the radio signal. Data communication takes place from the sensors via power supply lines of the light points. A central processing device is provided with warning means to generate a warning if the detected position of the vehicle is outside a predefined area at the airport which is permitted to the vehicle.
A sophisticated control system is utilized in a Space Shuttle Orbiter vehicle. The vehicle uses a conventional type of landing system having an aircraft tricycle configuration consisting of a nose landing gear and a left and right main landing gear. The nose landing gear is located in the lower forward fuselage, and the main landing gear is located in the lower left and right wing area adjacent to the mid-fuselage. The nose wheel is equipped with a ground proximity sensor, in order to determine Weight on Nosegear (WONG), a parameter required during landing. After landing, when WONG and other safety parameters have been established, Nose Wheel Steering (NWS) is enabled. One or more steering position transducers on the nose wheel strut transmit nose wheel steering position feedback to a comparison network so that the nose wheel commanded and actual positions may be compared for position error.
Braking is accomplished by a sophisticated system that uses electrohydraulic disk brakes with an anti-skid system. Only the two main gear sets have braking capability, and each can be operated separately. Two primary steering options are available. By applying variable pressure to the brakes, the crew can steer the vehicle by a method called differential braking. Also, by selecting nose wheel steering, the crew can use the rudder pedal assembly to operate an hydraulic steering actuator incorporated in the nose landing gear. The crew can also use the rudder to assist steering while at higher ground speeds.
Each main landing gear wheel has two speed sensors that supply wheel rotational velocity information to the skid control circuits in the brake/skid control boxes. The velocity of each wheel is continuously compared to the average wheel velocity of all four wheels. Whenever the wheel velocity of one wheel is a predetermined percentage below the average velocity of the four wheels, skid control removes brake pressure from the slow wheel until the velocity of that wheel increases to an acceptable range.
Motor-Generator machines able to provide high torque at low speed, which are small and compact, are disclosed in the art.
1. WO05112584 to Edelson discloses a motor-generator machine comprising a slotless AC induction motor. The motor disclosed therein is an AC induction machine comprising an external electrical member attached to a supporting frame and an internal electrical member attached to a supporting core; one or both supports are slotless, and the electrical member attached thereto comprises a number of surface mounted conductor bars separated from one another by suitable insulation. An airgap features between the magnetic portions of core and frame. Electrical members perform the usual functions of rotor and stator but are not limited in position by the present invention to either role. The stator comprises at least three different electrical phases supplied with electrical power by an inverter. The rotor has a standard winding configuration, and the rotor support permits axial rotation.
2. WO2006002207 to Edelson discloses a motor-generator machine comprising a high phase order AC machine with short pitch winding. In the following, H is the harmonic order of a waveform, N is the number of turns in a winding, and Δ is the span value of a mesh connected stator winding. Disclosed therein is a high phase order alternating current rotating machine having an inverter drive that provides more than three phases of drive waveform of harmonic order H, and characterized in that the windings of the machine have a pitch of less than 180 rotational degrees. Preferably the windings are connected together in a mesh, star or delta connection.
The term ‘winding’ therein refers to the group of all of the windings and/or coils and/or conductors of a single phase, unless otherwise specified. The winding that constitutes each phase consists of a ‘supply half’ and a ‘back half’. The ‘supply half’ is driven by the power supply, and has a phase angle dependent on the power supply phase or phases to which it is connected. The phase angle of the back half of each phase is equal to the phase angle of the supply half, offset by 180 ED. The pitch of a winding is the number of rotational degrees between the supply half of the winding and the back half of the winding.
Recommended therein is a way of making the winding shorter and at the same time making the magnetomotive force more sinusoidal, by using short pitch windings, and by distributing the winding over several slots. When the coils of the winding are distributed over several slots, there is a reduction in the combined induced electromotive force. The individual coils of each winding will have a different spatial orientation due to the slots and there will be a phase difference between them.
Concentrated windings may also be used, wherein the coils of each half of a winding are contained in one slot only.
A method for operating a high phase order induction motor is also disclosed therein, involving electrically connecting N windings into a mesh connection with a value of Δ that provides a substantial range in speed/torque relation when operating with at least two out of first, second and third harmonic, low order harmonics being the most efficient.
The above disclosure is further directed to selection of a winding pitch that yields a different chording factor for different harmonics. The aim is to select a chording factor that is optimal for the desired harmonics.
3. Disclosed in WO2006/065988 to Edelson is a motor-generator machine comprising stator coils toroidally wound around the inside and outside of a stator. The machine may be used with a dual rotor combination, so that both the inside and outside of the stator may be active. Even order drive harmonics may be used, if the pitch factor for the windings permits them.
Said coils may be connected in series or may be independent.
In one embodiment of this motor-generator machine, an AC electrical rotating apparatus is composed of: a rotor, a substantially cylindrically shaped stator that has one surface that faces the rotor, and a number of conductive coils. Each coil is disposed in a loop wound toroidally around the stator. A drive means, for example an inverter, provides more than three different drive phases to the coils. In a further embodiment, the machine is equipped with teeth or slots for lending firm support to said coils. The slots may be on the stator surface that faces the rotor or also on the opposite stator surface. In a preferred embodiment, each of the coils is driven by a unique, dedicated drive phase. However, if a number of coils have the same phase angle as one another, and are positioned on the stator in different poles, these may alternatively be connected together to be driven by the same drive phase. In a further alternative, where two coils or more have a 180 electrical degree phase angle difference between them, they may be connected in anti-parallel to the same drive phase.
The AC machine coils may be connected and driven in a number of ways, including but not restricted to: a star connection and a mesh connection. It is preferable that the drive means, for example, the inverter, be capable of operating with variable harmonic drive, so that it may produce the impedance effect. In one embodiment, the coils are connected with short pitch windings. In a preferred embodiment, the coils are connected to be able to operate with 2 poles, or four poles, under H=1 where H is the harmonic order of the drive waveform. The coils may be connected together in series, parallel, or anti-parallel.
4. In U.S. Patent Appl. Pub. No. 2006/0273686, a motor-generator machine is disclosed comprising a polyphase electric motor which is preferably connected to drive systems via mesh connections to provide variable V/Hz ratios. The motor-generator machine disclosed therein comprises an axle; a hub rotatably mounted on said axle; an electrical induction motor comprising a rotor and a stator; and an inverter electrically connected to said stator; wherein one of said rotor or stator is attached to said hub and the other of said rotor or stator is attached to said axle.
Such a machine may be located inside a vehicle drive wheel, and allows a drive motor to provide the necessary torque with reasonable system mass. In one embodiment the stator coils are wound around the inside and outside of the stator. In a further embodiment, the machine contains a high number of phases, greater than three. In a further embodiment, the phases are connected in a mesh connection. In a further embodiment, each half-phase is independently driven to enable second harmonic drive for an impedance effect. Improvements are apparent in efficiency and packing density.
5. WO06113121 discloses a motor-generator machine comprising an induction and switched reluctance motor designed to operate as a reluctance machine at low speeds and an inductance machine at high speeds. The motor drive provides more than three different phases and is capable of synthesizing different harmonics. As an example, the motor may be wound with seven different phases, and the drive may be capable of supplying fundamental, third and fifth harmonic. The stator windings are preferably connected with a mesh connection. The system is particularly suitable for a high phase order induction machine drive systems of the type disclosed in U.S. Pat. Nos. 6,657,334 and 6,831,430.
The stator of the induction/reluctance motor may be wound with any even number of poles. The rotor, in combination with the stator, is designed with a particular structure that reacts to a magnetic field configuration generated by one drive waveform harmonic. The reaction to this harmonic by the rotor structure produces a reluctance torque that rotates the rotor. For a different harmonic drive waveform, a different magnetic field configuration is produced, for which the rotor structure defines that substantially negligible reluctance torque is produced. However, this magnetic field configuration induces substantial rotor currents in the rotor windings, and the currents produce induction based torque to rotate the rotor.
In a further embodiment of the induction/reluctance motor, the rotor and stator each have a different high number of very small teeth. Magnetic poles are established to rotate the rotor. ‘Interference’, or ‘correlation’ between the stator and rotor teeth will tend to follow the magnetic poles, causing the rotor to move much more slowly than the magnetic poles.
In a further embodiment of the of the induction/reluctance motor, the rotor is structured to produce a substantial reluctance torque under operation of a first harmonic, and a negligible reluctance torque under operation of another harmonic. The harmonic that provides substantial reluctance torque is used to cause the motor to operate based on the reluctance principle, and a harmonic that provides negligible reluctance torque is used to drive the motor as an induction motor.
In a further embodiment of the induction/reluctance motor, the difference between the number of stator teeth and the number of rotor teeth is equal to half of the pole count of the developed magnetic field used to drive the rotor due to reluctance.
In a further embodiment of the induction/reluctance motor, the rotor is designed with a number of salient poles or flux guides that produces substantial reluctance torque under the operation of a magnetic field of a certain pole count, but produces negligible reluctance torque, and substantial inductance-based torque, under the operation of a second magnetic field with a second pole count. The two magnetic fields are set up in a stator, having more than three different phases per pole. Two different harmonics, that develop a different number of poles to one another, are used.
For a transition between the induction and reluctance effects, it is possible to separately generate two different harmonics. The rotor may be structured so that when driven by the harmonic producing the reluctance effect, the rotor rotates in the reverse direction to the rotating stator magnetic field. In order to enable the rotation of such a rotor to be in the same direction for both effects, the harmonic that produces one of the effects can be synthesized to cause magnetic field rotation in the opposite direction to the other harmonic. For example, the harmonic used to produce the reluctance effect is supplied to the stator windings in reverse phase order. Alternatively, the harmonic used to produce one of the effects could be a harmonic that produces a magnetic field that rotates in the reverse direction, such as the fifth harmonic in a 3-phase machine. However, a rotor could also be structured that rotates in the same direction as the rotating magnetic field. This is preferred, for one reason because any harmonic will generate for the rotor some level of inductance based torque, and it is preferable that this will be in the same direction to rotation.
In a further embodiment of the induction/reluctance motor, the stator windings are connected mesh. The span of the mesh is chosen according to the envisioned usage of the machine, since the span has an effect on the inductance of the machine when different harmonics are synthesized.
In further embodiments of the induction/reluctance motor, the stator windings may be wrapped in a toroidal fashion around the stator, the number of driven phases may be half the number of slots, each driven phase may be distributed amongst two adjacent slots, the number of driven phases may be equal to the number of slots, and/or each driven phase may be distributed amongst two adjacent slots.
In a further embodiment, a polyphase motor includes a drive unit to synthesize N phases of alternating current, where N is more than three per 180 degrees; and to select between applying a Type A and a Type B harmonic drive waveform for the N phases. The Type A and Type B harmonic drive waveforms each include at least one harmonic order that the other does not comprise. The polyphase motor also includes a stator and a rotor, in which the stator has N stator winding phases, driven by the drive unit; and the stator and rotor have profiles suited to produce substantial reluctance based rotor rotation when the Type A harmonic drive waveform is applied. The rotor has windings, suited for producing substantial inductance based rotor rotation when the Type B harmonic drive waveform is applied.
In a further embodiment, the invention describes a method for operating a motor capable of both inductance based and reluctance based operation. The method includes: providing a stator and rotor structure suitable for use as an induction motor, having both windings and a reluctance profile; supplying more than three different phases of alternating current to said stator, to rotate said rotor; and providing a selection of the following operational modes:
(i) supplying the alternating current to provide a stator magnetic field that produces a stator magnetic field matching the reluctance profile, and operable to rotate the rotor due to the reluctance effect,
(ii) supplying the alternating current to provide a stator magnetic field that is substantially inoperable to rotate the rotor due to the reluctance effect yet is operable to rotate the rotor due to the induction effect.